SPF and authenticated mail

[Chris Yuzik]

Alex Neuman van der Hans wrote:
> Or you can use port 587 on the same server using a different process 
> to receive mails that only allows authenticated users to use it.
Correct me if I'm wrong, but my understanding is that SPF checks are 
only done IF the inbound SMTP connection DOES NOT authenticate with the 
server. Same for RBL checks, etc. So why would anyone go to all this 
trouble?

Chris